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AU2007204599B2 - Improved operating strategies in filtration processes - Google Patents

Improved operating strategies in filtration processes Download PDF

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Publication number
AU2007204599B2
AU2007204599B2 AU2007204599A AU2007204599A AU2007204599B2 AU 2007204599 B2 AU2007204599 B2 AU 2007204599B2 AU 2007204599 A AU2007204599 A AU 2007204599A AU 2007204599 A AU2007204599 A AU 2007204599A AU 2007204599 B2 AU2007204599 B2 AU 2007204599B2
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AU
Australia
Prior art keywords
membrane
filtration
duration
membranes
cycles
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Ceased
Application number
AU2007204599A
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AU2007204599A1 (en
Inventor
Tina Nguyen
Roger William Phelps
Ashley Sneddon
Fufang Zha
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Evoqua Water Technologies LLC
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Evoqua Water Technologies LLC
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Filing date
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Priority claimed from AU2006900146A external-priority patent/AU2006900146A0/en
Application filed by Evoqua Water Technologies LLC filed Critical Evoqua Water Technologies LLC
Priority to AU2007204599A priority Critical patent/AU2007204599B2/en
Publication of AU2007204599A1 publication Critical patent/AU2007204599A1/en
Assigned to SIEMENS INDUSTRY, INC. reassignment SIEMENS INDUSTRY, INC. Amend patent request/document other than specification (104) Assignors: SIEMENS WATER TECHNOLOGIES CORP.
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Publication of AU2007204599B2 publication Critical patent/AU2007204599B2/en
Assigned to EVOQUA WATER TECHNOLOGIES LLC reassignment EVOQUA WATER TECHNOLOGIES LLC Request to Amend Deed and Register Assignors: SIEMENS INDUSTRY, INC.
Ceased legal-status Critical Current
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/12—Controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/22—Controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/24—Dialysis ; Membrane extraction
    • B01D61/32—Controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
    • B01D61/44—Ion-selective electrodialysis
    • B01D61/54—Controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/02—Membrane cleaning or sterilisation ; Membrane regeneration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/14—Pressure control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2313/00—Details relating to membrane modules or apparatus
    • B01D2313/48—Mechanisms for switching between regular separation operations and washing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/04—Backflushing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/18—Use of gases
    • B01D2321/185—Aeration

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  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Urology & Nephrology (AREA)
  • Nanotechnology (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • External Artificial Organs (AREA)

Abstract

A method of operating a membrane filtration system having a number of repeated operation cycles, the method including the step of varying the values of one or more operating parameters of the system associated with a particular operation cycle between and/or during one or more repetitions of the operation cycle. Membrane filtration systems operating in accordance with the method are also disclosed.

Description

-1l TITLE: Improved Operating Strategies in Filtration Processes TECHNICAL FIELD The present invention relates to cleaning of membranes in membrane 5 filtration systems and, more particularly, to operating strategies in such systems to reduce energy requirements. BACKGROUND OF THE INVENTION Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms 10 part of common general knowledge in the field. Reduction of operating energy and membrane fouling is a continued effort for the membrane system suppliers. In general, membrane fouling tends to be faster at a reduced energy input to clean the membrane. Different methods have been proposed to reduce the energy requirement without significant impact 15 on the membrane fouling. United States Patent Nos. 6,555,005 and 6,524,481 proposed an intermittent air scouring of the membranes instead of continuous air injection. In United States Patent Nos. 6,245,239 and 6,550,747, a specific cyclic aeration system was proposed to reduce the air consumption in cleaning membranes. The cyclic aerating system described in the prior art requires fast 20 responding valves to open and close at a high frequency and therefore wearing of valves is significant. DISCLOSURE OF THE INVENTION According to one aspect, the present invention provides a method of operating a membrane filtration system, the method including the steps of: 25 providing a plurality of repeated operation cycles, preferably filtration cycles; and alternating a value of one or more operating parameters of the system selected from the group consisting of scour gas flow-rate, filtration flux, and filtration cycle duration between predetermined values between repetitions of said operation cycles. 30 The method may also include adjusting filtration cycle time and/or other parameters according to the load to membranes. Preferably, the method includes the step of varying the duration of the operation cycle. For preference, the method may include varying the values of -2 one or more operating parameters instead of using constant values for such parameters. Such parameters may include but are not limited to, operating flux, transmembrane pressure and membrane scour air flow-rate. For preference, the variation includes alternating the value of the operating 5 parameter and/or the duration of the operating cycle between two or more predetermined values or durations. In one preferred form, the membrane filtration system includes at least two membranes or groups of membranes having distinct operating cycles, wherein the variation is alternated between said membranes or groups of membranes. For preference, said cycle duration may 10 be varied in dependence on an operating parameter value, for example, transmembrane pressure (TMP) or operating flux. Alternatively, said cycle duration may be varied according to the change of a performance related parameter, for example, an increase in TMP or a change of permeability/resistance. 15 According to another aspect, the present invention provides a method of operating a membrane filtration system, the method including the steps of: providing a plurality of repeated operation cycles, preferably filtration cycles, and alternating the duration of a particular operation cycle between predetermined values between repetitions of said operation cycles. 20 According to another aspect, the present invention provides a method of operating a membrane filtration system, the method including the steps of: providing a plurality of repeated operation cycles; and varying the values of one or more operating parameters of the system between predetermined values during repetitions of said operation cycles, the one or more operating 25 parameters including at least scouring gas flow rate; and varying a duration of the operation cycles based on the values of the one or more operating parameters. According to another aspect, the present invention provides a method of operating a membrane filtration system having a number of repeated operation 30 cycles, the method including the step of varying a frequency of cyclic alternating between a normal, non-zero, membrane scour air flow rate and a lower, non zero, membrane scour air flow rate, by varying a lower membrane scour air-flow - 2a duration as a multiple or sub-multiple of a normal membrane scour air-flow duration, independent of the filtration cycle, between one or more repetitions of an operation cycle consisting of said lower membrane scour air-flow duration and said normal membrane scour air-flow duration. 5 According to another aspect, the present invention provides a method of operating a membrane filtration system having a number of repeated operation cycles, the method including the step of varying a frequency of cyclic alternating between a normal, non-zero, membrane scour air flow rate and a lower, non zero, membrane scour air flow rate, by varying a lower membrane scour air-flow 10 duration as a multiple or sub-multiple of a normal membrane scour air-flow duration, independent of the filtration cycle, during one or more repetitions of an operation cycle consisting of said lower membrane scour air-flow duration and said normal membrane scour air-flow duration. According to further aspects, the present invention also includes apparatus 15 or membrane filtration systems configured to operate according to the inventive methods. BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 20 Figure 1 is a graph illustrating alternating air scour flow-rate; Figure 2 is a graph illustrating the effect of alternating gas scour flow-rate on membrane permeability; Figure 3 is a graph illustrating a comparison of the effect of constant and alternating gas scour flow-rate on membrane permeability; and 25 Figure 4 is a graph illustrating a comparison of membrane filtration performance (TMP) under different operating conditions. DESCRIPTION OF PREFERRED EMBODIMENTS Alternating operating parameters in filtration cycles A filtration cycle in a membrane filtration system typically includes filtration 30 stage and a backwash and/or relaxation stage. The method of one embodiment of the invention alternates the value of operating parameters between the WO 2007/079540 PCT/AU2007/000024 -3 filtration cycles. For systems which use gas scouring or aeration to clean the membranes, the operating parameters may include scour gas flow-rate, filtration flow-rate, or the like. For the scour gas, a normal gas flow-rate is used in one cycle and a lower or higher gas flow-rate for the next cycle in repeated cycles. 5 Such an operating strategy does not require any special valves, has little impact on the membrane fouling and does not affect the membrane's net production of filtrate. A typical filtration cycle in a membrane filtration system is in the range of 2 to 60 minutes for both drinking water and wastewater treatment, and more 10 typically in the range of 3 to 45 minutes. The scour gas flow-rate alternates between the two gas flow-rates. The lower gas flow-rate used is related to the membrane properties and the scour duration. For a typical filtration cycle the lower gas flow-rate may be any rate below 100% of the normal value, but is preferred to be at least 20% of the normal rate in order to achieve alternation 15 between filtration cycles and without significant impact on membrane fouling. Such an alternating strategy can also be applied to other operating parameters of the system, for example, the filtration flow-rate. The filtration flux may be operated at two different rates: one cycle at normal flux and the other cycle at a higher flux in repeated cycles. 20 In the practical applications of this embodiment, such an alternating of operating parameters between two cycles can be applied to two membrane modules, two membrane racks or two membrane cells. For example, one membrane cell can be operated at the normal scour gas flow-rate and the other one at a lower scour gas flow in repeated cycles. The net gas requirement for 25 the gas scouring is therefore reduced. Alternating scour gas flow-rate According to another embodiment of the invention, the operating strategy flexibly varies the gas scour alternating frequency independent of the filtration cycle. It is simply to choose the normal gas flow duration and lower gas flow 30 duration. It is preferred that the duration of lower gas flow is 0.5-5 times that for the normal gas flow. Figure 1 illustrates the airflow pattern according to the strategy of this embodiment. The lower gas flow rate can be any rate less than 100% of the WO 2007/079540 PCT/AU2007/000024 -4 normal value, but is preferred to be at least 10% of the normal value to avoid significant membrane fouling. In a network of membrane modules, this alternating strategy can be interchanged among corresponding sets of modules so that one set of modules 5 receives the normal gas flow and the other sets of modules get the lower gas flow. For example, the duration of lower gas flow may be set to twice that of the normal gas flow. Then the gas alternation may be applied to three sets of modules - one set receives the normal gas flow and the other two lower gas flow. 1o Adjusting filtration cycle time according to practical load to membrane One undesirable side effect of the gas saving strategy used above is the increase in membrane fouling during operation at peak flux that occurs in wastewater treatment. The membranes are under stressed condition and the reduced energy input achieved by scouring at a lower gas flow can make the 15 situation worse. To overcome this difficulty, the operating strategy is changed by reducing the duration of the filtration cycle. This is based on the principle that backwash or relaxation is dependent on the membrane's resistance rise, not on the fixed filtration time. The resistance rise rate will double or more when the membrane operating flux doubles. If the 20 filtration time is fixed to being the same as used with the normal flux, then the resistance rise will be significant at the higher flux operation, resulting in difficulty recovering the membrane performance through backwash or relaxation and leading to a continuous rise in the membrane resistance. However, if the filtration time is reduced, the membrane resistance rise is less and it is easier to 25 recover the membrane performance. The membrane resistance increase is a preferred indicator to determine the backwash or relaxation cycle requirements. Other parameters such as transmembrane pressure (TMP) increase and permeability decline may also be used as indicators to determine the necessity for a backwash/relaxation cycle. 30 For example, if the filtration time is 12 minutes at normal flux, the filtration time can be reduced to 6 minutes or less at a flux twice the normal one.
WO 2007/079540 PCT/AU2007/000024 -5 Example 1 This example demonstrates the effect of alternating gas flow on the membrane fouling. The example uses a membrane bioreactor system set up for municipal wastewater treatment. A membrane bioreactor module was installed 5 in a membrane tank. Mixed liquor from an aerobic tank was fed to the membrane tank at a flow rate of five times that of the filtrate flow rate (5Q) and the extra mixed liquor was circulated back to the aerobic tank. The MLSS concentration in the membrane tank was in the range of 10 -12 g/L. The membrane filtration was carried out in a filtration and relaxation mode and no 10 liquid backwash was used during operation of the system. The following operating condition was applied: 1. Standard operating condition: 12 minutes filtration and 1 minute relaxation with continuous gas (in this example, air) scouring at 9 m 3 /hr; 2. Alternating air flow-rate at 9 and 5 m 3 /hr in filtration cycles, that is, 13 15 minutes at 9 m 3 /hr air and 13 minutes at 5 m 3 /hr air. Figure 2 shows such an alternating pattern and the change of the membrane permeability with the air flow-rate. Figure 2 shows that at a lower scour gas flow-rate, the membrane fouled quickly and the permeability of membrane dropped sharply. However, the 20 permeability was largely recovered when the gas flow-rate was raised. An extended test was conducted and compared with the constant airflow in Figure 3. At the normal operating flux of 30 L/m 2 /hr, the membrane fouling rate was little changed under the alternating gas flow operation between 9 and 5 m 3 /hr. This example demonstrates that the membrane scour gas can be supplied 25 at alternating flow rates without impacting on the membrane fouling. In this example, the net gas supply required to effectively scour the membrane was reduced by 22%. Example 2 30 This example demonstrates how to change the operating strategy to cope with the peak flux operation. The membrane filtration system set-up was the same as in Example 1.
WO 2007/079540 PCT/AU2007/000024 -6 In this Example, the operating flux was increased by 50% from 30 to 45 L/m 2 /hr. Under such a high load condition, the operating transmembrane pressure (TMP) increases much faster during the filtration period. The situation becomes more stressed at the lower air flow-rate. Figure 4 shows the testing 5 result under different operating strategies. The transmembrane pressure (TMP) was increased by about 1 kPa during 12 minutes filtration cycle with a supply of scour air at a flow rate of 9 m 3 /hr, but increased by more than 3 kPa when the air flow rate was reduced to 5 m 3 /hr. The faster transmembrane pressure (TMP) rise indicates a rapid fouling of the membrane. The membrane fouling tends to 10 be more difficult to recover by relaxation, leading to a gradual consistent increase in TMP. If the filtration time is shortened to 6 minutes and relaxation is also reduced to 30 seconds then the TMP rises only about 1 kPa at the low airflow rate, making it easier to recover by relaxation. Figure 4 shows that an alternating air strategy could also be effectively applied at peak flux by 15 shortening the filtration cycle. It will be appreciated that further embodiments and exemplifications of the invention are possible without departing from the spirit or scope of the invention described.

Claims (29)

1. A method of operating a membrane filtration system, the method including the steps of: providing a plurality of repeated filtration cycles; and 5 alternating a value of one or more operating parameters of the system selected from the group consisting of scour gas flow-rate, filtration flux, and filtration cycle duration between predetermined values between repetitions of said filtration cycles.
2. A method according to claim 1 including adjusting the predetermined 10 values of the one or more operating parameters according to a load to membranes of the membrane filtration system.
3. A method according to claim 1 or claim 2 including varying the values of the one or more operating parameters during a repetition of the filtration cycles.
4. A method according to any one of the preceding claims wherein the 15 membrane filtration system includes at least two membranes or groups of membranes having distinct filtration cycles and wherein alternating the value of the one or more operating parameters includes alternating the value of the one or more operating parameters between said membranes or groups of membranes. 20
5. A method of operating a membrane filtration system, the method including the steps of: providing a plurality of repeated filtration cycles; and alternating a duration of a particular filtration cycle between predetermined values between repetitions of said filtration cycles. 25
6. A method according to claim 5 wherein the membrane filtration system includes at least two membranes or groups of membranes having distinct filtration cycles and wherein alternating the duration of the filtration cycles includes alternating the duration of the operation cycles between said membranes or groups of membranes. 30
7. A method according to any one of claims 1 to 4, wherein the duration of the filtration cycles is varied in dependence on an operating parameter value.
8. A method according to any one of claims 1 to 4, wherein the filtration cycle duration is varied in dependence on transmembrane pressure (TMP). -8
9. A method according to any one of claims 1 to 4, wherein the filtration cycle duration is varied in dependence on filtration flux.
10. A membrane filtration system comprising: means for operating said system with a number of repeated filtration cycles 5 and; control means configured to alternate a value of one or more operating parameters of the system selected from the group consisting of scour gas flow rate, filtration flux, and filtration cycle duration between predetermined values between repetitions of said filtration cycles. 10
11. A membrane filtration system according to claim 10, wherein the duration of the filtration cycles is varied in dependence on an operating parameter value.
12. A membrane filtration system according to claim 10, wherein the filtration cycle duration is varied in dependence on transmembrane pressure (TMP).
13. A method according to claim 10, wherein the filtration cycle duration is 15 varied in dependence on filtration flux.
14 A membrane filtration system according to any one of claims claim 10 to 13 wherein said control means is configured to adjust the values of the one or more operating parameters according to a load to membranes of the membrane filtration system. 20
15. A membrane filtration system according to any one of claims 10 to 14 wherein the membrane filtration system includes at least two membranes or groups of membranes having distinct filtration cycles and wherein alternating the value of the one or more operating parameters includes alternating the value of the one or more operating parameters between said membranes or groups of 25 membranes.
16. A method of operating a membrane filtration system having a number of repeated operation cycles, the method including the step of varying a frequency of cyclic alternating between a normal, non-zero, membrane scour air flow rate and a lower, non-zero, membrane scour air flow rate, by varying a lower 30 membrane scour air-flow duration as a multiple or sub-multiple of a normal membrane scour air-flow duration, independent of the filtration cycle, between one or more repetitions of an operation cycle consisting of said lower membrane scour air-flow duration and said normal membrane scour air-flow duration. -9
17. A method of operating a membrane filtration system having a number of repeated operation cycles, the method including the step of varying a frequency of cyclic alternating between a normal, non-zero, membrane scour air flow rate and a lower, non-zero, membrane scour air flow rate, by varying a lower 5 membrane scour air-flow duration as a multiple or sub-multiple of a normal membrane scour air-flow duration, independent of the filtration cycle, during one or more repetitions of an operation cycle consisting of said lower membrane scour air-flow duration and said normal membrane scour air-flow duration.
18. A method according to claim 16 or claim 17 including adjusting the 10 frequency of cyclic alternating between a normal membrane scour air flow rate and a lower membrane scour air flow rate according to the load to membranes.
19. A method according to claim 16 or claim 17 including the step of varying the duration of a filtration cycle comprising a filtration period and a relaxation period. 15
20. A method according to claim 16 or claim 17 wherein the normal membrane scour air flow rate and the lower membrane scour air flow rate are of predetermined values.
21. A method according to any one of claims 16 to 20 wherein the membrane filtration system includes at least two membranes or groups of membranes 20 having distinct operation cycles and wherein the variation of membrane scour air flow rate is alternated between said membranes or groups of membranes.
22. A method according to claim 16 or claim 17 wherein said duration of the operation cycle or cycles is varied in dependence on an operating parameter value. 25
23. A method according to claim 22 wherein the operating parameter is transmembrane pressure (TMP).
24. A method according to claim 22 wherein the operating parameter is operating flux.
25. A membrane filtration system operated in accordance with the method of 30 any one of claims 16 to 24.
26. A membrane filtration system operating with a number of repeated operation cycles including control means for varying a frequency of cyclic alternating between a normal membrane scour air flow rate and a lower - 10 membrane scour air flow rate, by varying a lower membrane scour air-flow duration as a multiple or sub-multiple of a normal membrane scour air-flow duration, independent of the filtration cycle, between one or more repetitions of an operation cycle consisting of said lower membrane scour air-flow duration 5 and said normal membrane scour air-flow duration.
27. A membrane filtration system operating with a number of repeated operation cycles including control means for varying a frequency of cyclic alternating between a normal membrane scour air flow rate and a lower membrane scour air flow rate, by varying a lower membrane scour air-flow 10 duration as a multiple or sub-multiple of a normal membrane scour air-flow duration, independent of the filtration cycle, during one or more repetitions of an operation cycle consisting of said lower membrane scour air-flow duration and said normal membrane scour air-flow duration.
28. A method of operating a membrane filtration system substantially as 15 herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
29. A membrane filtration system substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 20
AU2007204599A 2006-01-12 2007-01-12 Improved operating strategies in filtration processes Ceased AU2007204599B2 (en)

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Application Number Priority Date Filing Date Title
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Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
AU2006900146A AU2006900146A0 (en) 2006-01-12 Improved operating strategies in filtration processes
AU2006900146 2006-01-12
PCT/AU2007/000024 WO2007079540A1 (en) 2006-01-12 2007-01-12 Improved operating strategies in filtration processes
AU2007204599A AU2007204599B2 (en) 2006-01-12 2007-01-12 Improved operating strategies in filtration processes

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AU2007204599B2 true AU2007204599B2 (en) 2012-06-28

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EP (1) EP1986767A4 (en)
JP (1) JP2009523062A (en)
KR (1) KR20080085906A (en)
CN (1) CN101370568A (en)
AU (1) AU2007204599B2 (en)
CA (1) CA2634150A1 (en)
NZ (1) NZ569210A (en)
SG (1) SG168522A1 (en)
WO (1) WO2007079540A1 (en)

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